The subject invention generally concerns the field of electronic instruments and accessories therefor. The subject invention specifically addresses the problem of providing forward and backward compatibility between these instruments and devices.
The first oscilloscope probes simply conveyed the signal at the tip to the oscilloscope connected to the probe. No additional features were provided. In the early 1970""s, the 7000-series oscilloscope probe was introduced by Tektronix, Inc. of Beaverton, Oreg. In addition to conveying the voltage at it""s tip to the host oscilloscope, this probe provided two additional capabilities, channel identification and scale factor indication. The scale factor indicator feature is implemented by applying an analog encoded through a resistor of a predetermined value to a slip ring in the probe. The instrument senses the voltage on the slip ring and adjusts the vertical sensitivity accordingly to automatically accommodate 1xc3x97, 10xc3x97, or 100xc3x97 probes. The channel identification feature temporarily grounds the slip ring through a momentary switch mounted on the probe and operated by the user. Probes incorporating these features are said to exhibit level 1 capability.
The next generation of probes, introduced by Tektronix, Inc. in 1986, accompanied the 11,000-series oscilloscopes. These probes included a power hook-up through the connector. They also included an accessory offset hook-up through the connector with calibrated offset operation at the accessory input. A serialized, expandable I2C coding capability for communication through the connector to indicate function, scale factor, offset, and accessory type was also provided. Probes having these capabilities are said to exhibit level 2 capability. Level 2 capable instruments are also backward compatible with level 1 probes.
It is well known to provide backward compatibility between instruments and older generation probes, as demonstrated by fact that the above-mentioned Level-2 capable 11,000-series oscilloscopes accept and use the Level-17,000 series probes.
Clearly, each new generation of oscilloscopes and probes provides new and ever more useful features for the user. Unfortunately, current generation oscilloscopes will not be able to recognize the codes and provide proper operation for features which did not exist at the time the current oscilloscopes were manufactured. Of course, some software implementable features may be added to current oscilloscopes by downloading new code, but if a new feature requires new hardware, then the current oscilloscope will not be able to exercise the desired function. Moreover, it is foreseeable that if the current oscilloscope receives a command to exercise a function of which it has no knowledge, then a situation may be created in which an attempt to exercise the function may cause damage to the oscilloscope or to the probe. What is needed is a way to establish forward compatibility between currently produced oscilloscopes and next generation of probes and accessories.
An accessory or a probe for a test and measurement instrument includes an input for receiving a signal and an output coupled to said test and measurement instrument, and at least one signal path for conveying a signal from the input to the output. The accessory or probe also includes a data path for communicating between the test and measurement instrument and the accessory, and a memory unit for storing information about said accessory, the memory unit being coupled to the data path.
The information includes an entry concerning a function that the test and measurement instrument is required to be capable of controlling. The memory unit retrieves that entry under control of the test and measurement instrument and conveys the entry to the test and measurement instrument via the data path for a determination by the test and measurement instrument as to whether or not the test and measurement instrument can control the function.